Vibration at 1700-1900 RPM

[tech10002]

My truck started an irritating vibration a couple months ago from 1700-1900 RPM. It won't do it while you're sitting still, only while it's loaded under power. I've went over the exhaust, heat shield, up pipes, down pipe, etc. with a fine tooth comb, and can't find anything that appears to be too close or rubbing.

Is there anything common I might be overlooking? This is really annoying. You can feel the buzzing noise in the floor and hear it momentarily every time you stop and start again once it passes those RPMs, and if you keep it in that RPM range, it will do it constantly.